Fbxo18-mediated proteasomal degradation in the process of aging. The ubiquitin-mediated degradation of protein targets has established roles in diverse cellular processes including DNA replication and repair, regulation of transcription, metabolic control, and apoptosis. The dysregulation or breakdown of many of these essential pathways has been implicated in the process and pathology of aging. Currently, a mechanistic understanding of how targeted proteolysis contributes to the aging phenotype is largely unknown. The central objective of this application is to define the mechanisms through which Fbxo18, an uncharacterized E3 ubiquitin ligase identified by alternative screening methods as a putative regulator of longevity, contributes to aging-related processes. We have identified novel substrates of Fbxo18 using tandem affinity purification and mass spectrometry techniques refined and validated in our laboratory, and the degradation of the complex of substrates identified forms the basis of this proposal. Aim 1 will confirm and characterize biochemically the degradation of these novel substrates by Fbxo18. Concurrently, Aim 2 will establish the biological significance of Fbxo18-mediated degradation of these substrates and will describe a phenotype for defective Fbxo18-mediated proteolysis. Aim 2 will seek to establish a functional role for Fbxo18 in cellular processes related to aging, notably recovery from replication stress and DNA damage. The results of Aims 1 and 2 will converge to elucidate novel regulatory pathways for these cellular processes. Such regulatory pathways are potential sites of therapeutic intervention in the treatment of aging-related diseases.